A new study from Queen Mary University of London and the Norwegian School of Sports Sciences investigated how the human body responds to seven days of water-only fasting.Researchers monitored 12 healthy volunteers, analyzing roughly 3,000 proteins in their blood before, during, and after fasting.

While the body quickly shifted from burning glucose to using fat within the first two to three days, major molecular changes did not occur until after day three.

More than one-third of the proteins tracked showed significant changes, particularly those related to the extracellular matrix, which supports organs and neurons in the brain.Participants lost an average of 5.7 kilograms (12.5 pounds), mainly fat, with lean tissue largely recovered after resuming food.

Genetic analysis suggested that the fasting-induced protein shifts could influence long-term health, potentially improving metabolic, neurological, and immune function.

However, researchers also noted risks, such as increased inflammation, blood clotting changes, and the need for medical supervision during prolonged fasting, especially for individuals with underlying health conditions.

These findings highlight that some of fasting’s most pronounced biological effects require several days without calories, offering a molecular explanation for fasting’s potential health benefits and inspiring future therapies that could mimic these effects without extreme dietary restriction.